Handheld Gas Detector Communication Protocol
This protocol is designed for the communication of ATO handheld series of gas detectors. It is fully compatible with the MODBUS RTU standard protocol. It is also suitable for other instruments that use serial ports (UART, RS232, RS485) and USB-to-serial function.Change the gas type table based on V0.0.
1. Serial port settings:
Baud rate: 2400/4800/9600/19200/38400/115200 (generally the default is 9600) Start bit: 1 bit
Data bits: 8 bits
Parity: 1 bit even parity/no parity Stop bit: 1 bit
2. Communication protocol:
The communication protocol follows the MODBUS-RTU standard protocol and adopts a question-and-answer communication method. When the communication data of the master (host computer or PC, the same below) is sent to the slave, the slave (detector, the same below) first determines whether the address of the local machine is It is consistent with the address code, and the data is received only when the address code matches (except the broadcast address), until the frame data is stopped, and the check code is checked. If it is correct, the corresponding task is executed, and then the execution result is returned to the host; If an error occurs, an abnormal response will be returned to remind the host to send again;
3. Data format
The data format follows the MODBUS-RTU standard format. Each frame of data is divided into address code, function code, data area and check code, as shown below:
Start Address
code
Function code
Data area Check code End
4 byte periods 1 byte 1 byte N bytes 2 bytes 4 byte periods
1)Start and end:
Follow the MODBUS-RTU standard format, there is no specially established start and end bytes, the instrument (including master and slave, the same below) detects the gap time of 4 byte cycles, it is the end of the previous frame of data and the next The start of frame data; for example, when the baud rate is 9600, the period of each byte is about 1 millisecond, and the period of 4 bytes is 4 milliseconds. Taking into account the timing error of the instrument, to ensure normal communication, it is recommended to send the frame interval is more than 5 milliseconds, and the byte interval in the same frame is within 2 milliseconds;
2) Address code:
The address code is one byte, which is the first byte of each data frame, from 0 to 255. The address byte indicates that the slave with the address set by the user will receive the information sent by the master. Each slave must have a unique address code, and only the slaves that match the address code can respond to the echo. When the slave sends back information, the equivalent address code indicates where the information comes from. 0 means the broadcast address, all slaves can receive data.
3) Function code:
The function code is one byte, which is the second byte of each data frame. It will indicate that the master tells the slave to perform the corresponding task; when the read operation (function code 03 or 65), the slave will return a band Message with specified information; when writing operation (function code 06), a successful operation will return a null data (that is, the data length byte is 0) information, if the operation fails, an exception message will be returned.
The function codes supported by this protocol are as follows:
Code Meaning Operation
03 Read data register Read the contents of the specified register 06 Write data register Modify the contents of the specified register
65 Read history
record
Read the history record of the specified number
255 Abnormal
response
Only when the slave returns an exception code when it is abnormal
4) Data area:
The data area contains actions to be performed by the slave or information sent back by the slave. For master sending and slave return, the length is not equal. When the master sends, the length of the data area is fixed at 4 bytes. When the slave returns, the length of the data area is variable; the format of the data area is as follows:
Host send (function code 03)
1 byte 2 bytes 3 bytes 4 bytes
Address high byte
Address low byte
Quantity high byte Quantity low byte
Note: This protocol only supports reading and writing of a single register, so bytes 3 and 4 can only be 0x0001, and other data is invalid.
Host send (function code 06)
1 byte 2 bytes 3-4 bytes 5-6 bytes 7-8 bytes 9-10 bytes
Address high byte Address low byte Channel 1 data Channel 2 data Channel 3 data Channel 4 data
Note: The channel data is high byte first and low byte last; character data is filled with 0 in the high byte.
Host send (function code 65)
1 byte 2 bytes 3 bytes 4 bytes
Numbering highest byte Numbering second highest byte Numbering second lowest byte Numbering lowest byte
Return from the machine (general)
1 byte 2 bytes 3 bytes 。。。。。。 N+1 bytes
Data length byte Data1
Handheld Gas Detector Communication Protocol
Return from the machine (function code 65)Byte 1 2 3 4 5 6 7 8 9 10 11 。。。。。。 N*2+6 N*2+7
Data Data length Y
ea r m on th da y ho ur m in ut e se co nd Channel 1 Channel 2 。。。。。。 Channel N
Note: The data length and time data are of unsigned character type, and the data of all channels are of unsigned integer type, with the high byte first.
The slave returns abnormally (function code 255)
1 byte 2 bytes
Data length (fixed to 0x01) Exception code (see definition of exception code)
5) Check code:
The master or slave can use the check code to judge whether the received information is wrong. Due to electronic noise or some other interference, the information may change during the transmission process. The error check code ensures that the master or slave does not work on the error information during the transmission. This increases the safety and efficiency of the system. This protocol complies with the MODBUS-RTU standard, and the error check uses 16-bit redundant cyclic code (CRC-16), and the high byte of the data in the CRC code is sent and received first.
4. The attached table
1) Definition of data register address: Addr
ess
Name Return data type Data
length
Return data content Remarks
0x02 Total number
of channels
Unsigned character type
1 byte Total number of valid
channels of the slave
Read only
0x03 Total number
of records
Unsigned long integer
4 bytes Total number of stored
history records
Read only
0x10 Gas type Unsigned
character type
Number of channels* 1
Gas type of all channels See definition of gas type
0x11 Data unit Unsigned
character type
Number of channels* 1
Data unit of all channels See gas unit
definition 0x12 Data decimal places Unsigned character type Number of channels* 1
Data decimal places of all channels
integer of channels* 2 0x14 Gas ADC value Unsigned integer Number of channels* 2
ADC value of all channels Read only 0x15 Gas concentration value Unsigned integer Number of channels* 2 Concentration values of all channels Read only 0x16 Low gas value Unsigned integer Number of channels* 2 Underreported value of all channels 0x17 High gas value Unsigned integer Number of channels* 2
High value of all channels
Note: All channel data is channel 1 first, and the high byte is first when the data type is integer.
All data related to gas concentration (including gas range, concentration and alarm value) must be combined with the data unit and data decimal places to get the final value; for example, the concentration value is 1234, the unit value is 4, and the decimal place value is 1. Together it means that the gas concentration value is 123.4mg/m3.
2) Gas type definition:
Unsigned char GASTY[65][10]= {
"GAS ","CO ","H2S ","O2 ","EX ", //0-4 "SO2 ","NH3 ","H2 ","N2 ","O3 ", //5-9 "TVOC ","CL2 ","HCL ","NO ","NO2 ", //10-14 "PH3 ","AsH3 ","HCN ","CO2 ","SF6 ", //15-19 "Br2 ","HBr ","F2 ","HF ","N2O ", //20-24 "H2O2 ","NOX ","SOX ","Odor ","VOC ", //25-29 "CH4 ","C2H6 ","C3H8 ","C4H10 ","iC4H10 ", //30-34 "C5H12 ","C2H4 ","C3H6 ","C4H8 ","iC4H8 ", //35-39 "CH4O ","C2H6O ","C3H8O ","iC3H8O ","C4H10O ", //40-44 "CH2O ","C2H4O ","C3H6O ","C3H4O ","C2H2 ", //45-49 "C6H6 ","C7H8 ","C8H10 ","C8H8 ","C6H6O ", //50-54 "ETO ","C2H8O2 ","NMHC ","GAS ","GAS ", //55-59 "U-DEF1 ","U-DEF2 ","U-DEF3 "," U-DEF4 ","GAS ", //60-64 };
Handheld Gas Detector Communication Protocol
3) Definition of gas unit:
Value 0 1 2 3 4 5+
symbol PPM PPB %VOL %LEL Mg/m3 Reserved
4) Exception code definition：
Value 0 1 2 3 4 5 6+ signific ance Unkno wn Calibratio n error
Data error Comman d error Instrum ent busy Instrumen t failure Reserved
Note: Data errors include errors in the data area such as register address error, register number out of range, historical record number out of range, etc.
Command error means that the function code is not within the error range of the slave. 5) CRC code calculation method:
The steps to calculate the CRC code are:
Step 1: Preset the 16-bit register as hexadecimal FFFF (that is, all 1). Call this register CRC register; Step 2: XOR the first 8-bit data with the low bit of the 16-bit CRC register, and put the result in the CRC register;
Step 3: Shift the contents of the register one bit to the right (toward the low bit), fill the highest bit with 0, and check the lowest bit;
Step 4: If the lowest bit is 0: repeat step 3 (shift again);
If the lowest bit is 1: CRC register is XORed with polynomial 0xA001;
Step 5: Repeat steps 3 and 4 until the right shift is 8 times, so that the entire 8-bit data is processed; Step 6: Repeat steps 2 to 5 to process the next 8-bit data;
When all the data information is processed, the CRC register finally obtained is the CRC code. The C language example of CRC code calculation is as follows:
//---//
//Function name：Get CRC check code
//Function function: calculate the CRC checksum,
//Input variable: pSendBuf-data area address nEnd-data length //Output variable: wCrc-checksum
//---//
unsigned int GetCRC(unsigned char *pSendBuf, unsigned char nEnd) {
unsigned char i,j;
unsigned int wCrc = (unsigned int)(0xffff); for(i = 0;i<nEnd;i++)
{
wCrc ^= (unsigned int)(pSendBuf[i]); for(j = 0;j<8;j++)
{
if(wCrc&0x01) {
wCrc ^= 0xA001; } else wCrc >>=1; } } return wCrc; }